1. Field of the Invention
The present invention relates to a method and system for plating objects. More particularly, the present invention relates a plating method and system for substantially maintaining byproduct concentrations and/or plating component concentrations in a plating cell. An additional aspect of the invention relates to the reuse of at least some plating components and the monitoring of organic material in various substances.
2. Description of Related Art
Semiconductor chips are typically manufactured in a process involving the plating of metal components onto wafers. Due to a recent shift toward copper interconnect technology, plating techniques are being developed for plating wafers with copper material. Current copper plating processes, however, require costly consumable substances and generate a relatively significant amount of waste material that is costly to dispose and presents a number of environmental concerns.
In one conventional copper plating technique, wafers are plated in a cell filled with plating substances including both inorganic and organic additives. The inorganic additives include copper sulfate, sulfuric acid, water, and possibly hydrochloric acid.
Generally, the organic additives are categorized as either suppressors or accelerators, depending on their role in the electroplating process. As their names imply, suppressors act to impede the deposition of metallic copper on the cathodic surface, while accelerators enhance the deposition. Suppressors can be further characterized as either carriers or levelers. The suppressors are generally polymeric surfactants. In the case of carriers, they form a mono-layer at the cathode which offers a diffusion barrier to cupric ions, and enhances cathodic polarization needed for fine grain structure. Levelers are typically multiple-charged and adhere preferentially to highly charged areas such as corners and edges, and thus prevent overhanging at trench mouths. The large size of levelers impedes their migration into trenches, which in turn impedes conformal filling and allows for better bottom-up filling.
As mentioned above, organic additives also include accelerators. These substances are usually unsaturated compounds containing a polar sulfur, oxygen, or nitrogen functional group. They adsorb strongly and uniformly on seed surfaces, promoting dense nucleation and, consequently growth of fine grains. This leads to a uniformly smooth, well-textured (i.e. bright) finish. Accordingly, accelerators are often referred to as brighteners.
During a plating process, organic additives break down, with the accelerators generally tending to break down more rapidly than suppressors. In a simplified approach, it has been estimated that at least one commercially available plating chemistry has accelerator agents with a stoichiometric breakdown rate estimated at 2 mg/amp-hr while its suppressor agents break down at a rate of 10 mg/amp-hr.
Since organic materials break down during plating, a substantially continuous plating process requires some way of controlling levels of the organic additives in the plating cell. In addition, there is a need to control the levels of byproducts that are generated as a result of the breakdown of the organic additives.
The simplest approach to controlling levels of organic additives and their byproducts involves batch processing where a plating cell is initially filled with fresh plating substances and plating of wafers continues until the results become unacceptable. Then, the entire contents of the cell are drained and the cell is refilled again with fresh plating substances. This generates large quantities of waste, which must be treated because the waste contains relatively large amounts of copper and acid. Since this batch processing does not have direct control over the chemistry of the plating bath, a number of potentially reusable components from the drained cell are disposed without being reused.
Another approach to controlling organic additives and their byproducts is referred to as the xe2x80x9cbleed and feedxe2x80x9d approach. In bleeding and feeding, fresh plating substances are continuously added to the plating cell at a continuous flow rate while a portion of the contents are continuously drained from the cell at a constant flow rate and then disposed without being reused. Although this approach is slightly more sophisticated than the batch approach, both methods lead to substantially the same amount of waste generated over time. For example, the amount of waste could range from 10 cc/wafer to 25 cc/wafer at high wafer plating rates. In addition, while the bleed and feed approach does remove some of the contaminants associated with the break down of the organic additives, it does not completely remove them, and only dilutes them somewhat to a generally steady-state concentration. Over a period of time, the accumulation of the byproducts requires a complete draining of the plating cell and subsequent refilling.
In light of the foregoing, there is a need in the art for improving plating methods and systems.
Accordingly, the present invention is directed to a method and system that may substantially obviate one or more of the limitations of the related art. In particular, the present invention is directed to methods and systems that have particular advantages associated with the plating of copper onto wafers. The invention, in its broadest sense, however, could be used for plating of a wide variety of different substances onto a wide variety of different objects. For example, the present invention could be used for plating objects with gold.
In one aspect, the invention includes a method of plating objects. In one method according to the invention, plating substances are added to a plating cell. Objects are placed in the plating cell and plated in the plating cell. Plated objects are removed from the plating cell. Used plating substances, including at least one byproduct, are drained from the plating cell. At least one aspect associated with the plating of the objects is monitored. Based on the at least one monitored aspect, the flow rate of the plating substances added to the plating cell and/or the flow rate of the used plating substances drained from the plating cell are adjusted.
In one preferred practice of the method, at least one byproduct of at least one of the plating substances is created during the object plating, and the monitored aspect is related to the creation of the at least one byproduct. The flow rate adjustment(s) substantially maintain(s) a concentration of the at least one byproduct in the plating cell below a predetermined level.
In another preferred practice of the method, the amount of at least one component of the plating substances is reduced during the plating of the objects, and the monitored aspect is related to the reduction in amount of the at least one component of the plating substances during the plating. The flow rate adjustment(s) substantially maintain(s) a concentration of the at least one component in the plating cell above a predetermined level.
In yet another aspect of the method, the used plating substances are processed to convert at least part of the used plating substances into reusable plating substances. The reusable plating substances are added to the plating cell.
The monitored aspect is preferably chosen from the number of objects plated in the plating cell, the time elapsed during the plating of the objects, current density and/or electrical energy applied during the plating, idle time elapsed when the plating does not occur, the amount of agitation of substances in the plating cell, the amount of pulse plating occurring during the plating, temperature of substances in the plating cell, temperature of the plating cell, the deposition rate of material plated on the objects, the electrical conductivity of the material plated on the objects, the concentration of carbon in the material plated on the objects, the degree of void-free plating in trenches of the objects, and the chemical composition of the plating substances.
In another method according to the present invention, at least one byproduct of at least one of the plating substances is created during the plating of the objects. Used plating substances, including the at least one byproduct, are drained from the plating cell. The used plating substances are purified to remove at least some of the at least one byproduct and thereby create purified plating substances. At least one component is combined with the purified plating substances to create a mixture of plating substances. The mixture of plating substances is passed into the plating cell to thereby reuse the purified plating substances.
In one aspect, the at least one byproduct includes organic material, and the method further includes monitoring the level of organic material in the purified plating substances.
In another aspect, the level of organic material in the mixture of plating substances is monitored.
In addition, the method could further comprise adjusting, based on the monitored level of organic material, the amount of the at least one component combined with the purified plating substances.
In yet another aspect, the mixture of plating substances is passed into a storage tank, and the mixture in the storage tank is monitored to determine the level of organic material.
In still another aspect, multiple plating cells are provided and a separate storage tank is associated with each of the plating cells. The method further includes monitoring organic material in each storage tank substantially simultaneously. The organic material in each storage tank is preferably monitored via a separate sensing probe in each storage tank and a common controller receiving a respective signal from each sensing probe.
The purifying preferably includes at least one of filtering the used plating substances with activated carbon, filtering the used plating substances with at least one ion exchange medium compound, filtering the used plating substances with a particle removal filter, exposing the used plating substances to ultraviolet light, heating the used plating substances, exposing the used plating substances to at least one chemical oxidizing substance, and degassing the used plating substances. In the preferred embodiment, the purifying includes removing substantially all plating substances containing organic material, and the at least one component includes organic material.
In a further aspect of the invention, each object is a wafer configured to be a component of a semiconductor, and each wafer is plated with copper.
The invention also includes a system for use in plating objects. In one aspect, the system is configured to be used with a plating cell configured to plate objects. The plating cell is associated with means for adding plating substances to the plating cell, and means for draining used plating substances from the plating cell. The system includes at least one monitor configured to monitor at least one aspect associated with the plating of the objects. A controller is in electrical communication with the monitor. The controller is configured to control at least one of the adding means and the draining means, based on said at least one monitored aspect, to adjust at least one of the flow rate of the plating substances added to the plating cell, and the flow rate of the used plating substances drained from the plating cell.
In one aspect of the system, the used plating substances include at least one byproduct of at least one of the plating substances, and the byproduct is created during plating of the objects in the plating cell. The monitored aspect is related to the creation of the at least one byproduct, and the flow rate adjustment(s) provided by the controller substantially maintain(s) a concentration of the at least one byproduct in the plating cell below a predetermined level.
In another aspect of the system, the amount of at least one component of the plating substances is reduced during plating of objects in the plating cell. The monitored aspect is related to the reduction in amount of the at least one component of the plating substances during the plating, and the flow rate adjustment(s) provided by the controller substantially maintain(s) a concentration of the at least one component in the plating cell above a predetermined level.
The adding means and/or the draining means could include at least one of a pump and a flow control valve. The controller is preferably configured to control the pump(s) and/or flow control valve(s).
The system could further include a processing unit configured to convert at least part of the used plating substances into reusable plating substances, the reusable plating substances being reused in the plating cell.
The monitor is preferably configured to monitor at least one of the number of objects plated in the plating cell, the time elapsed during the plating of the objects, current density and/or electrical energy applied during the plating, idle time elapsed when the plating does not occur, the amount of agitation of substances in the plating cell, the amount of pulse plating occurring during the plating, temperature of substances in the plating cell, temperature of the plating cell, the deposition rate of material plated on the objects, the electrical conductivity of the material plated on the objects, the concentration of carbon in the material plated on the objects, the degree of void-free plating in trenches of the objects, and the chemical composition of the plating substances.
Another aspect of the invention involves a system including a purifier and a component combiner. The purifier is configured to purify the used plating substances to remove at least some of the at least one byproduct and thereby create purified plating substances. The component combiner is configured to combine at least one component with the purified plating substances to create a mixture of plating substances. The mixture of plating substances is passed into the plating cell to thereby reuse the purified plating substances.
In an additional aspect, the system includes a purified substance monitor configured to monitor the level of organic material in the purified plating substances.
Another aspect includes a mixture monitor configured to monitor the level of organic material in the mixture of plating substances.
Preferably, the system further comprises a controller in electrical communication with the monitor. The controller controls the component combiner, based on the monitored level of organic material, to adjust the amount of the at least one component combined with the purified plating substances.
In one other aspect, the system includes probes configured to be positioned in separate storage tanks so that organic material in separate tanks can be monitored separately, and a common controller receiving a respective signal from each sensing probe.
In an even further aspect, the purifier is configured to provide at least one of filtering the used plating substances with activated carbon, filtering the used plating substances with at least one ion exchange medium compound, filtering the used plating substances with a particle removal filter, exposing the used plating substances to ultraviolet light, heating the used plating substances, exposing the used plating substances to at least one chemical oxidizing substance, and degassing the used plating substances.
Another aspect relates to a structural arrangement and/or a plating method, wherein the following equation is satisfied:       C          b      ,              t        ⁢                  xe2x80x83                ⁢        2              =            C              b        ,                  t          ⁢                      xe2x80x83                    ⁢          0                      +                            (                                    t              ⁢                              xe2x80x83                            ⁢              2                        -                          t              ⁢                              xe2x80x83                            ⁢              1                                )                V            xc3x97              (                              m            b                    -                                    η              b                        ·                          dV              p                        ·                          C                              b                ,                                  t                  ⁢                                      xe2x80x83                                    ⁢                  1                                                                    )            
wherein
Cb, t2=byproduct concentration at time t2,
Cb, t1=byproduct concentration at time t1,
Cb, t0=initial plating solution byproduct concentration,
V=volume of plating substances in at least one of the plating cell and a storage tank associated with the plating cell,
mb=mass rate of byproduct build up,
dVp=liquid flow rate through the purifier, and
xcex7b=byproduct removal efficiency of the purifier.
A further aspect relates to a structural arrangement and/or plating method, wherein the following equation is satisfied:       C          c      ,              t        ⁢                  xe2x80x83                ⁢        2              =            C              c        ,                  t          ⁢                      xe2x80x83                    ⁢          0                      +                            (                                    t              ⁢                              xe2x80x83                            ⁢              2                        -                          t              ⁢                              xe2x80x83                            ⁢              1                                )                V            xc3x97              (                                                            V                c                            ·              q              ·              dt                                      (                                                t                  ⁢                                      xe2x80x83                                    ⁢                  2                                -                                  t                  ⁢                                      xe2x80x83                                    ⁢                  1                                            )                                -                      m            c                    -                                    h              c                        ·                          dV              p                        ·                          C                              c                ,                                  t                  ⁢                                      xe2x80x83                                    ⁢                  1                                                                    )            
wherein
Cc, t2=component concentration at time t2,
Cc, t1=component concentration at time t1,
Cc, t0=initial plating solution component concentration,
Vc=flow rate of component introduction,
q=component density,
dt=time interval of component introduction,
mc=mass rate of component consumption during the plating, and
hc=component removal efficiency of the purifier.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.